To use the StaffTraveler eSIM, your device must be eSIM compatible. You can find the list of supported devices here. You can also verify whether your phone supports eSIM by checking the device settings.
For Android devices:
Go to your phone's settings > “Connections” > “SIM Manager”
For iOS devices:
Go to your phone's settings > “Mobile Service”
If you see an option to add an eSIM, your device is eSIM compatible.